1. Field of the Invention
This invention relates to the use of esters or partial esters of aromatic, cycloaliphatic and aliphatic polycarboxylic acids with phenyl polyglycol ethers substituted by aryl, alkyl or aralkyl groups for the preparation of coal/water suspensions.
2. Description of the Prior Art
Aqueous coal (dust) slurries have been the subject of increasing interest because of their ease in handling in transport and their good combustion/gasification characteristics when coal is used as an energy carrier or a chemical raw material.
With respect to both long-distance transport and the energy balance of such suspensions in the combustion process, it is of interest to prepare suspensions which are as high in solids content as possible but which possess as low a viscosity as possible and are stable via-a-vis sedimentation and shear stress.
Polymers and polycondensates, such as polysaccharides, carboxymethylcellulose, gum arabic, xanthan gum, guar gum or copolymers, and others have been successfully used in the prevention of premature sedimentation.
There have been many efforts to reduce viscosity for a given water content by the addition of additives or to increase the solids contents of suspensions for a given viscosity.
The following surface-active substances have been proposed for this purpose: anionic surfactants--U.S. Pat. No. 4,282,006, U.S. Pat. No. 4,302,212, U.S. Pat. No. 4,330,301, U.S. Pat. No. 4,304,572, Japanese Pat. No. 030963; nonionic surfactants--European Pat. No. 0,132,712-A, European Pat. No. 0,013,146-A, European Pat. No. 0,008,628, Swedish Pat. No. 002,878, Swedish Pat. No. 002,879, U.S. Pat. No. 4,276,054, European Pat. No. 0.109,740-A, European Pat. No. 0,057,576; and zwitterionic surfactants--WO-A No. 83/03618.
Mixtures of the above types have been frequently proposed, for example in European Pat. No. 0,057,576.
The proposed additives for the coal/water slurries are of varying effectiveness with respect to viscosity reduction and stability vis-a-vis sedimentation and effects of shear stress, depending on the type, origin and processing of the coal used.
Although numerous additives have been proposed, a need continues to exist for new additives for coal/water slurries with increased effectiveness in reducing viscosity and maintaining stability with respect to sedimentation and the effects of shear stress.